Growth of human hepatocytes in response to regenerative stimuli or in neoplastic conditions is a phenomenon manifested in all forms of human hepatic disease. Loss of hepatic parenchyma due to any toxins or chemical carcinogens or inflammatory conditions results in regenerative response aimed to restore the organ mass. In hepatic neoplasms (hepatocellular carcinoma, adenoma). abnormal growth is the hallmark of the neoplastic phenotype. Very recently, we have been able to purify and characterize the human Hepatopoietin A and the human Hepatopoietin B. These substances stimulate hepatocyte proliferation in serum free cultures. In addition, we found that ECGF stimulates proliferation of a subset of rat hepatocytes and is a strong mitogen for human hepatocytes. We have also adapted the 2% DMSO protocol and succeeded in setting up a cyclic system in which DNA synthesis can be turned off and on. This allows multiple periods of DNA synthesis in hepatocytes in culture (with multiple cell cycles per period). Human hepatocytes, in contrast to rat hepatocytes, respond poorly to EGF, respond stronger to ECGF and maintain better differentiation in culture. This proposal aims to characterize the response of normal and neplastic human hepatocytes to these growth factors and growth inhibitors such as TGFbeta and IL-6. Expression of the growth factors and their receptors by human hepatocytes will also be examined in human liver needle biopsies. These studies will be extended to cover the behavior of human hepatocytes transplanted in ECGF- impregnated endothelialized collagen sponges. The effect of chemical carcinogen initiators and tumor promoters will also be examined in this transplantation system.